Simple DC Electric Motor

This simple direct current electric motor is built from the following materials:
14 gauge insulated copper wire (~3ft)
1 nickel-plated neodymium hard drive magnet or large ceramic magnet (fridge magnet is too weak)
2 large wood screws
2 small wood screws
2 tie wraps or twist ties
Nail polish (just a few dabs)
1 D battery
1 block of scrap wood for the base

The coil is made from 2ft of 14 gauge insulated copper wire which came from a 14-2 romex spool.  Using the D battery, wrap the insulated wire around the battery in tight loops leaving a about two inch tail on each side.  In our case we wrapped the wire around the battery 4.5 times as shown.

Make the tails on each side of the coil as straight and parallel as possible.  The tails should form an imaginary continuous line (or axle) which will be the axis of rotation about which the circular coil will turn.  Use tie wraps or twist ties to wrap the coil in place on each side where the tail starts.  Clip each tail to about 1.5in.

Strip about 3/4in of the insulation off of each end of tail and give the end a an angled bend up on the left side and down on the right as shown here (this will help keep the coil from sliding off the bracket when rotating).

Now use the nail polish to carefully paint just the top side of the right (or left) stripped wire tail.

Next is the task of creating the brackets out of stripped copper wire. They are made from two approximately 6in lengths of 14 gauge stripped copper wire which is screwed into the wood base with two large round-head wood screws.  This wire is stiff enough that it will make contact with the battery terminals adequately without having to add a rubber band etc., and it is also stiff enough to keep its shape went bent in a particular way.

Carefully shape each bracket side so that the tails of the coil can be rested into an S-shape cradle and will form an axis of rotation that is parallel to the wood base.

Next is the magnet placement.  The neodymium magnet should be arranged to produce maximum rotation of the coil.  You may have to experiment with this for a few minutes before securing the magnet to the wood base.  (If the magnet is not secured, the magnetic field resulting from the current flowing through the coil will push the magnet out of position and end the motor's rotation.)

The coil is placed about 1/16in above the magnet center on the magnet as shown.

Here is a simplified diagram of the magnetic field (B) in red produced by the magnet and the current (I) produced through the coil by the battery and bracket assembly.

Using Fleming's Left Hand Rule for motors, the associated force produced upon a particular portion of the coil is orthogonal to both the field (B) and current  (I)

With the coil oriented vertically, you only need to give the coil a rotational push in either direction to produce sustained rotation.  Each side of the coil will "feel" a force which points in opposite directions resulting in continued rotation.  (Again here the magnetic field is red, current is turquoise, and force is green)

The nail polish is necessary to block current from flowing for the portion of the rotation which would produce opposing forces and stop continued rotation.


Here is our simple dc electric motor in action.